See the links in the first post. You may have to click on the camera name in the right pane. The linked chart clearly shows the noise issue on the E-M5 between ISO 200 and 400.

Various posts over the years have said that the Panasonic sensor used by the earlier Pens tends to have less noise when you use the full stop ISO's (200, 400, 800, 1600, 3200) rather than the intermediate versions. There is an option to only use whole stops in auto ISO. It sounds like the same is probably true of the Sony sensor used in the E-M5, E-PL5, and E-PM2.

I may remember poorly, but I think I read once (somewhere in the forum) that 160, 320, 640, 1280, etc. Were the appropriate full stops on the GH2. And I had inferred from that that those were the ones to focus upon on the G5. If this is wrong, I'd like clear word on that

You are largely (though not exactly) right about the GH2 whose only "real" ISOs are 160, 320, 640, and 800.

I don't think that it is clear that ISO=800 on the GH2 is unmanipulated. See bg2b's OP here:

Real ISOs are probably just 160, 320, and 640. 200, 400, and 800 show odd artifacts (gaps or near gaps) in the RAW histograms. 250, 500, and 1000 show them even more. Everything beyond ISO 1000 is completely artificial; they're obviously just digital scalings of lower ISOs.

I calculated the number of EV that certain ISOs (from rated ISO=160 through ISO=800) deviate from a straight line projection (in EV) from that which would be derived from multiplying the Read/Dark Noise data by the ratio of the Saturation ISO divded by Saturation ISO=167.

The intermediate ISOs between these are accomplished by means of digitally scaling the RAW values upwards rather than by analog amplification. The same is true about any ISO above 800. It follows that using any ISOs other than those I listed will not bring you any benefits above using the next lower ISO among those listed. They will be the same for read noise but worse for the risk of highlight clipping.

Whether the G5 behaves the same way, I don't know. And I am not sure anyone else here does either at this point. You can find out for yourself by using RawDigger and inspect the histogram for different ISOs. If digital scaling is employed, there will be gaps in the histogram (i.e., certain specific ADU values will not occur). See here for example: